Generally, in image forming devices such as copy machines, printing devices, facsimiles, or the like, that use electrophotographic methods, light based on an image read by an image scanner, is irradiated by an exposing device onto a surface of a photoreceptor that is an image holding body, an electrostatic latent image of this image is formed, and after that, toner is attached to this electrostatic latent image by a developing device, to form a toner image. After the toner image is transferred by a transferring device onto a paper sheet, the paper holding the toner image is sandwiched and fed into a nip formed by a pressure roller and a heat roller arranged in a fixing device, and the toner image is fixed to the paper by heating and pressurizing.
Furthermore, in recent years, with a view towards energy saving, fixing devices are proposed in which, by reducing diameters of the heat roller and the pressure roller in the fixing devices, with regard to heating quantity of a heat source for heating the heat roller, the heat quantity of the heat roller and the pressure roller is made relatively small. More specifically, for example, a fixing device is disclosed that is provided with a heat roller consisting of a small sized hollow roller made of metal with an external diameter of 15 mm or less and a wall thickness of 1 mm or less, and a small sized pressure roller having an elastic layer with an external diameter of 15 mm or less.
Here, as in the abovementioned conventional fixing device, when the diameters of the heat roller and the pressure roller are made small, it becomes difficult to ensure the width of the nip formed by the heat roller and the pressure roller. Consequently, implementing measures such as reducing the hardness of the elastic layer of the pressure roller, increasing the pressurizing force of the pressure roller acting on the heat roller, or the like, are necessary. However, in conditions with these types of measure implemented, if the pressure roller is in continuous pressurized contact with the heat roller, due to insufficient strength of the elastic layer of the pressure roller, or the like, as shown in FIG. 11, an end face 53a of the elastic layer 53 of the pressure roller 52 in contact with the heat roller 51 (that is, an end face in a longitudinal direction X of the pressure roller 52) bends. Thus, the end face 53a protrudes outwards, in the abovementioned longitudinal direction X, in comparison to a state before the pressure roller 52 is put in pressurized contact with the heat roller 51, as shown in FIG. 12. As a result, since tearing forces act on a joining face 56 of the elastic layer 53 and a shaft 55, as shown in FIG. 11, cracking 54 occurs in the abovementioned end face 53a, towards the joining face 56 of the elastic layer 53 and the shaft 55, and a problem arises in that the operating life of the pressure roller 52 becomes short.
Consequently, the present invention was made in view of the abovementioned problems, and has as an object the provision of a fixing device and an image forming device equipped with the same, that has a simple structure, that avoids occurrences of cracking in the elastic layer of the pressure roller, and in which the pressure roller has a long operating life.